sometimes, it's what's un-said. for all the talk this year about jobs and taxes, the growing national debt, medicare, healthcare, israel and iran, there are some very important issues that barely are being mentioned at all. what are they? my colleague, jeffrey brown of the pbs newshour, details a few. >> it's been hot this year - very hot: in fact, the federal government says the first half of 2012 was the hottest since recordkeeping began in the 1890s. it's been dry, extremely dry. the midwest suffered through its worst drought in almost 60 years. and it's been just plain weird with tornados in, of all places, brooklyn and queens. and of course, this weeks massive "frankenstorm." in fact, if you "google" "2012 unusual" the very first thing that pops up in the search field is "2012 unusual weather." >> no one can say with certainty what's behind all of this. but most scientists agree that extreme weather is becoming more common, a consequence of climate change caused by greenhouse gas emissions. it's a problem that